[petsc-users] Trying to understand -log_view when using HIP kernels (ex34)

[Dave May]

Thank you Barry and Junchao for these explanations. I'll turn on
-log_view_gpu_time.

Do either of you have any thoughts regarding why the percentage of flop's
being reported on the GPU is not 100% for MGSmooth Level {0,1,2} for this
solver configuration?

This number should have nothing to do with timings as it reports the ratio
of operations performed on the GPU and CPU, presumably obtained from
PetscLogFlops() and PetscLogGpuFlops().

Cheers,
Dave

On Fri, 19 Jan 2024 at 11:39, Junchao Zhang <junchao.zhang at gmail.com> wrote:

> Try to also add -log_view_gpu_time,
> https://petsc.org/release/manualpages/Profiling/PetscLogGpuTime/
>
> --Junchao Zhang
>
>
> On Fri, Jan 19, 2024 at 11:35 AM Dave May <dave.mayhem23 at gmail.com> wrote:
>
>> Hi all,
>>
>> I am trying to understand the logging information associated with the
>> %flops-performed-on-the-gpu reported by -log_view when running
>>   src/ksp/ksp/tutorials/ex34
>> with the following options
>> -da_grid_x 192
>> -da_grid_y 192
>> -da_grid_z 192
>> -dm_mat_type seqaijhipsparse
>> -dm_vec_type seqhip
>> -ksp_max_it 10
>> -ksp_monitor
>> -ksp_type richardson
>> -ksp_view
>> -log_view
>> -mg_coarse_ksp_max_it 2
>> -mg_coarse_ksp_type richardson
>> -mg_coarse_pc_type none
>> -mg_levels_ksp_type richardson
>> -mg_levels_pc_type none
>> -options_left
>> -pc_mg_levels 3
>> -pc_mg_log
>> -pc_type mg
>>
>> This config is not intended to actually solve the problem, rather it is a
>> stripped down set of options designed to understand what parts of the
>> smoothers are being executed on the GPU.
>>
>> With respect to the log file attached, my first set of questions related
>> to the data reported under "Event Stage 2: MG Apply".
>>
>> [1] Why is the log littered with nan's?
>> * I don't understand how and why "GPU Mflop/s" should be reported as nan
>> when a value is given for "GPU %F" (see MatMult for example).
>>
>> * For events executed on the GPU, I assume the column "Time (sec)"
>> relates to "CPU execute time", this would explain why we see a nan in "Time
>> (sec)" for MatMult.
>> If my assumption is correct, how should I interpret the column "Flop
>> (Max)" which is showing 1.92e+09?
>> I would assume of "Time (sec)" relates to the CPU then "Flop (Max)"
>> should also relate to CPU and GPU flops would be logged in "GPU Mflop/s"
>>
>> [2] More curious is that within "Event Stage 2: MG Apply" KSPSolve,
>> MGSmooth Level 0, MGSmooth Level 1, MGSmooth Level 2 all report "GPU %F" as
>> 93. I believe this value should be 100 as the smoother (and coarse grid
>> solver) are configured as richardson(2)+none and thus should run entirely
>> on the GPU.
>> Furthermore, when one inspects all events listed under "Event Stage 2: MG
>> Apply" those events which do flops correctly report "GPU %F" as 100.
>> And the events showing "GPU %F" = 0 such as
>>   MatHIPSPARSCopyTo, VecCopy, VecSet, PCApply, DCtxSync
>> don't do any flops (on the CPU or GPU) - which is also correct
>> (although non GPU events should show nan??)
>>
>> Hence I am wondering what is the explanation for the missing 7% from "GPU
>> %F" for KSPSolve and MGSmooth {0,1,2}??
>>
>> Does anyone understand this -log_view, or can explain to me how to
>> interpret it?
>>
>> It could simply be that:
>> a) something is messed up with -pc_mg_log
>> b) something is messed up with the PETSc build
>> c) I am putting too much faith in -log_view and should profile the code
>> differently.
>>
>> Either way I'd really like to understand what is going on.
>>
>>
>> Cheers,
>> Dave
>>
>>
>>
>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20240119/b4ec1b71/attachment-0001.html>